Hinged rotor blade to provide passive variable pitch

ABSTRACT

A hinged propeller comprising a hub and one or more blades is disclosed. In various embodiments, a blade is connected to the hub via a hinge, wherein at least a substantial part of the blade has a longitudinal axis that is substantially parallel to a line extending radially from a center of the hub, and wherein the hinge has an axis of hinge rotation that is oriented at a non-zero acute angle to a line that is perpendicular, in a plane of rotation of the hub, to said longitudinal axis.

CROSS REFERENCE TO OTHER APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/218,894 entitled HINGED ROTOR BLADE TO PROVIDE PASSIVE VARIABLE PITCHfiled Mar. 31, 2021, which is a continuation of U.S. patent applicationSer. No. 16/379,588, now U.S. Pat. No. 10,994,828, entitled HINGED ROTORBLADE TO PROVIDE PASSIVE VARIABLE PITCH filed Apr. 9, 2019, which is acontinuation of U.S. patent application Ser. No. 15/589,858, now U.S.Pat. No. 10,301,008, entitled HINGED ROTOR BLADE TO PROVIDE PASSIVEVARIABLE PITCH filed May 8, 2017, all of which are incorporated hereinby reference for all purposes.

BACKGROUND OF THE INVENTION

A variable pitch propeller is a propeller capable of being rotated aboutits longitudinal axis to vary the blade pitch. In aviation applications,a variable pitch propeller may be used to control the pitch of apropeller blade as it rotates, as in helicopter rotors, e.g., to controldirection of flight, increase efficiency, and/or the amount of thrust(or lift) generated.

Typically, the pitch of a variable pitch propeller is controlled by amechanical linkage and/or hydraulics. A control system typically is usedto control the elements that vary the pitch. Such mechanisms may becomplicated and may require frequent maintenance from highly skilledtechnicians. In addition, the mechanisms add weight, which results inhigher fuel costs, or shorter battery life and therefore flight time inthe case of an electric motor driven rotor, and which may make suchpropellers impractical for applications in which the additional weightis prohibitive.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the followingdetailed description and the accompanying drawings.

FIG. 1A is a diagram illustrating an embodiment of a rotor comprising ahinged blade to provide passive variable pitch.

FIG. 1B shows the propeller 100 of FIG. 1 from a side view in a verticalflight (e.g., hover) mode of operation.

FIG. 1C shows the same propeller 100 and associated elements in aforward flight orientation and mode.

FIG. 1D shows the blade 102 of FIG. 1 from a side view in a verticalflight (e.g., hover) mode of operation.

FIG. 1E shows the same blade 102 in a forward flight orientation andmode.

FIG. 2A is a diagram illustrating an embodiment of a rotor comprising ahinged blade to provide variable pitch.

FIG. 2B shows a side view the propeller 200 of FIG. 2A in ahover/vertical flight orientation and mode.

FIG. 2C shows the propeller 200 in a forward flight orientation andmode.

FIG. 3 is a diagram illustrating an embodiment of a tilt rotor aircraftin which a rotor comprising a hinged blade to provide variable pitch maybe used.

FIG. 4 is a state diagram illustrating an embodiment of a flight controlsystem such as may be used in an embodiment of an aircraft having arotor comprising a hinged blade to provide variable pitch.

DETAILED DESCRIPTION

The invention can be implemented in numerous ways, including as aprocess; an apparatus; a system; a composition of matter; a computerprogram product embodied on a computer readable storage medium; and/or aprocessor, such as a processor configured to execute instructions storedon and/or provided by a memory coupled to the processor. In thisspecification, these implementations, or any other form that theinvention may take, may be referred to as techniques. In general, theorder of the steps of disclosed processes may be altered within thescope of the invention. Unless stated otherwise, a component such as aprocessor or a memory described as being configured to perform a taskmay be implemented as a general component that is temporarily configuredto perform the task at a given time or a specific component that ismanufactured to perform the task. As used herein, the term ‘processor’refers to one or more devices, circuits, and/or processing coresconfigured to process data, such as computer program instructions.

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. The scope of the invention is limited only by the claims andthe invention encompasses numerous alternatives, modifications andequivalents. Numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theinvention. These details are provided for the purpose of example and theinvention may be practiced according to the claims without some or allof these specific details. For the purpose of clarity, technicalmaterial that is known in the technical fields related to the inventionhas not been described in detail so that the invention is notunnecessarily obscured.

A hinged rotor blade to provide passive variable pitch is disclosed. Invarious embodiments, a rotor includes one or more blades at least asubstantial portion of which extend radially from a central hub or nosesection of the rotor. The blade(s) is/are connected to the hub or nosesection via a hinge mechanism, such as a pin hinge, oriented at an acuteor other angle to a tangent to the hub or nose section. The orientationof the hinge pin or other axial member of the hinge mechanism results inthe hinged blade rotating back and inward, when viewed from a vantagepoint in front of the leading edge of the blade, as the forces acting onthe blade (e.g., thrust/lift, centrifugal force) change, e.g., as thepropeller and/or aircraft transition from a substantially horizontalorientation (e.g., hover or vertical flight) to a substantially verticalorientation (e.g., forward flight). The above-described rotation of theblade results in the pitch of the blade changing as the orientationand/or forces acted on the blade change, thereby exhibiting variablepitch without requiring the mechanical and/or hydraulic mechanismsmentioned above.

FIG. 1A is a diagram illustrating an embodiment of a rotor comprising ahinged blade to provide passive variable pitch. In the example shown,propeller 100 includes a blade 102 coupled to a central hub 104 via ahinge connection 106, 108. In the example shown, the hinge includes apin 106 that runs through a transverse hole in the end of blade 102nearest hub 104 and through holes on tab portions of a blade mounted 108attached fixedly to hub 104. The hinge 106, 108 in various embodimentsenables blade 102 to fold back towards a central axis of hub 104, e.g.,when no force is being applied to rotate propeller 100. Examples of hub104 include without limitation nose cone or other aerodynamically shapedhubs commonly found on propellers.

FIG. 1B shows the propeller 100 of FIG. 1 from a side view in a verticalflight (e.g., hover) mode of operation. As shown in FIG. 1B, as thepropeller 100 rotates in a substantially horizontal plane, a combinationof centrifugal force and thrust/lift force causes the blade 102 to moveoutward from a central (z) axis of propeller 100 and to sweep upwardfrom the horizontal plane, about 10 degrees up in the example shown. Insome embodiments, an upper physical stop, such as an end of a notch innosecone 104 that allows the blade 102 to sweep upward only to a pointat which the blade 102 engages the stop, may prevent the blade 102 fromsweeping up (as shown) beyond the point associated with the stop. FIG.1D shows the blade 102 of FIG. 1 from a side view in a vertical flight(e.g., hover) mode of operation. In the deployed position shown in FIG.1B, in hover/vertical flight blade 102 moves through the air at arelatively shallow pitch, e.g., about 5 degrees, as shown in the sidecross-section view of blade 102 to the right of the middle drawing inFIG. 1B. In the example shown, in this first stable position andassociated pitch, during hover/vertical flight the angle of attack ofthe blade 102 relative to oncoming airflow (represented by the blackarrow to the far right of FIG. 1D) is as shown.

FIG. 1C shows the same propeller 100 and associated elements in aforward flight orientation and mode. In the example shown, the propeller100 has been rotated to a forward flight position and mode in which thepropeller 100 rotates in a substantially vertical plane and advancesthrough the air in a forward direction associate with the tip andcentral (z) axis of nosecone 104. For example, the entire aircraft mayhave rotated (e.g., a tail sitter aircraft) or the propeller and/or awing on which it is mounted may have been rotated (e.g., tilt rotor ortilt wing aircraft). In the forward flight mode, for the same rotationalspeed (e.g., RPM) the propeller 100 generates less thrust than at thesame rotational speed in hover/vertical flight, while experience thesame centrifugal forces. As a result, the dihedral angle of the blade102 relative to the (substantially vertical) plane of rotation of thepropeller 100 decreases, e.g., to 5 degrees in the example shown. FIG.1E shows the same blade 102 in a forward flight orientation and mode. Atthis relatively lower dihedral angle, as shown in FIG. 1C, given theorientation of the hinge joint (106, 108) the blade 102 rotates backabout its longitudinal axis and as a result its pitch increasespassively, e.g., to 10 degrees in the example shown in FIG. 1E. Theresult is a lower angle of attack with respect to net oncoming airflow(black arrow a far right of FIG. 1E, the airflow comprising theresultant flow associated with the propeller turning—horizontalcomponent as shown—and the entire aircraft moving forward downwardvertical component as shown), relative to the hover mode andorientation, which enables the propeller to generate the (relativelylower) thrust required for forward flight without stalling.

Referring further to FIG. 1A, in the example shown, the axis of rotationof the hinge 106, 108 is offset from a line perpendicular to alongitudinal axis of the blade 102 by an acute angle (i.e., >0 degreesbut <90 degrees). As a result of this offset, blade 102 when viewed froma point in front of a leading edge of blade 102 (associated with point“A” in the example shown), rotates back around its longitudinal axis asthe dihedral angle (relative to the plane of rotation of the propeller100) decreases, resulting in pitch varying passively as the dihedralangle is changed, such as by changing from a hover/vertical flightorientation and mode to a forward flight orientation and mode(transition from FIG. 1B to 1C) or vice versa.

FIG. 2A is a diagram illustrating an embodiment of a rotor comprising ahinged blade to provide variable pitch. In the example shown in FIG. 2 ,propeller 200 includes a blade 202, 204 that has a primary airfoilportion 202 that extends radially from a central hub 206. In variousembodiments, a longitudinal axis of primary airfoil portion 202 may becoincident with or run parallel to a line extending radially from acenter of hub 206. The primary airfoil portion 202 is coupled to the hub206 via an angled neck portion 204 coupled to the hub 206 via a hinge208. In this example, the hinge 208 has a rotational axis (e.g., a pinor other axel) that is offset by an acute angle, in the x-y plane (i.e.,the plane of the page as shown in the top drawing in FIG. 2 ), from aline perpendicular to the longitudinal axis of primary airfoil portion202.

FIG. 2B shows a side view the propeller 200 of FIG. 2A in ahover/vertical flight orientation and mode. As shown in FIG. 2B, inhover/vertical flight the blade 202 of propeller 200 is at a relativelyhigher dihedral angle Y (gamma) and presents a relatively shallow pitch.

FIG. 2C shows the propeller 200 in a forward flight orientation andmode. In forward flight, the blade 202 rotates back and inward (compareFIG. 2B with FIG. 2C), similarly to the example shown in FIGS. 1A-1C,passively varying the pitch of the blade, as illustrated in this exampleby the change in position of point B relative to point A, and theincreased amount of the bottom side of the propeller blade (crosshatched areas in middle and bottom drawings) visible as the blade foldsback on its hinge 208.

As illustrated in FIG. 2A, in the example shown, the neck portion 204suspends the primary airfoil portion 202 at a distance from the hinge208, the distance being determined by a length of the next portion 204,in a direction orthogonal to the rotational axis of the hinge 208. Invarious embodiments, the length and shape of the neck portion 204 may beselected to achieve a desired degree of change in the pitch (angle ofattack) of the primary airfoil portion 202 associated with acorresponding amount of rotation about the axis of rotation of the hinge208.

In various embodiments, techniques disclosed herein may be used to varypassively the overall pitch of a propeller comprising a twisted blade,the fixed pitch of which is different at different points along thelength of the blade. In some embodiments, blade twist may be taken intoconsideration in determining the effect of varying the overall pitch ofa blade passively as disclosed herein.

In various embodiments, propellers comprising blades that are hinged asdisclosed herein, i.e., at an offset from a line perpendicular to alongitudinal axis of at least a primary airfoil portion of the blade,may be used to provide passively varied pitch in the context ofvertical/short takeoff and landing aircraft, including withoutlimitation tilt rotor, tilt wing, and tail-sitter type aircraft. Suchaircraft may use one or more propellers/rotors to provide lift in avertical or hover mode of flight, and may use the same one or morepropellers/rotors to provide thrust in a forward flight mode. In thevertical/hover mode, the rotors may be used to generate the relativelyhigh amount of lift force that may be needed to take off or landvertically and/or maintain the aircraft in a hover. In thehover/vertical flight orientation and mode of operation, the blades of apropeller as disclosed herein in various embodiments experience aresultant force that causes them to be deployed to a dihedral angle atwhich they are oriented at a relatively lower pitch (than in forwardflight, for example), which may be optimal to provide lift in thevertical flight or hover mode. By contrast, in the forward flight mode,in various embodiments the propeller blades may shift passively to aposition at a lower dihedral angle, at which the blade pitch is higherthan in the hover/vertical flight mode, to generate thrust to sustainforward flight and translate the aircraft to a desired destination. Insome embodiments, the thrust required for forward may be on the order ofone tenth that required for vertical flight/hover.

In various embodiments, the shape and materials of the blades and theangle at which the hinge is oriented are selected such that in forwardflight the blades rotate back about their longitudinal axes to aposition in which their respective pitch changes passively to a higherpitch (than in hover/vertical flight).

FIG. 3 is a diagram illustrating an embodiment of a tilt rotor aircraftin which a rotor comprising a hinged blade to provide variable pitch maybe used. In the example shown, a tilt rotor aircraft 300 is shown inthree stages of flight. In a first stage the aircraft 300 a is showntaking off in a vertical flight mode. In a next stage, the aircraft 300b is shown transitioning from the vertical flight mode (300 a) to aforward flight mode (300 c).

In the example shown, the rotors on the wing tips of the aircraft 300are shown to rotate from a vertical position (300 a) to an intermediateposition (300 b) as the aircraft transitions to forward flight, andfinally to a horizontal position (300 c) as the aircraft flies inforward flight. In a tilt wing aircraft, the rotors may remain in afixed position on the wings, and the wings may transition throughvertical and intermediate positions during takeoff and ultimately to ahorizontal position for forward flight. In a tail sitter type aircraft,the entire aircraft, excepting in some embodiments a cockpit portion,may rotate from a vertical to a transitional and finally to a forwardflight orientation, with both the wings and rotors remaining in a fixedposition relative to the airframe. In all three types of aircraft,significantly more thrust may be required to be generated duringtakeoff, hover, and/or landing, as applicable, than during forwardflight. In some embodiments, up to ten times the thrust/lift may need tobe generated in vertical flight and/or hover.

In various embodiments, passively variable pitch propellers as disclosedherein may be used in aircraft such as the tilt rotor aircraft shown inFIG. 3 and/or tilt wing or tail sitter type aircraft described above. Inthe vertical flight mode, as during takeoff as shown in FIG. 3 , therotors generate the thrust required for vertical flight, and in such anorientation and mode the resultant (net) force on the blades may besufficient to deploy the blades fully to a first stable position havinga first pitch. In forward flight, the rotors may fold back (lower butstill positive dihedral angle, for example) to a second stable positionhaving a second pitch more optimal for forward flight.

In some embodiments, a propeller blade may be hinged at an angle suchthat the leading edge is nearer a center/central rotational axis of thehub/nosecone than the trailing edge. In such embodiments, a position ofthe blade at a higher dihedral angle would have a higher pitch than at alower dihedral angle, i.e., opposite of the examples shown in FIGS.1A-2C.

FIG. 4 is a state diagram illustrating an embodiment of a flight controlsystem such as may be used in an embodiment of an aircraft having arotor comprising a hinged blade to provide variable pitch. In someembodiments, a flight control system may implement the state diagram 400of FIG. 4 . In some embodiments, a flight control system of a verticaltakeoff and landing aircraft, such as the tilt rotor aircraft of FIG. 3, may implement the state diagram of FIG. 4 . In the example shown, aflight control system and/or aircraft implementing the state diagram ofFIG. 4 is in a non-flight state 402, e.g., is landed on the ground withthe rotors not rotating or rotating at an idle speed. The aircraft maytransition via take off to a first stable propeller state 404, in whichto propeller is in a substantially horizontal orientation associatedwith vertical flight (e.g., takeoff, hover, landing). As a result, inthe first stable propeller state 404 the blades may be (more) fullydeployed to a position associated with a first pitch. The aircraft maytransition to a forward flight mode in which the propeller blades may bein a second stable state 406 associated with forward flight, and mayrotate passively to a second stable position having a second pitch thatis higher than the first pitch associated with the first stableposition.

The reverse sequence of states and transitions may be exhibited as theaircraft transitions from the forward flight mode/state (406) to thevertical flight mode/state (404), e.g., to prepare for landing, and fromthe vertical flight mode/state to the landed and/or idling state (402)as the aircraft lands. In the latter state, the propeller blades mayfold back further or fully (if shutdown) on their hinges.

Techniques disclosed herein may be used to provide a variable pitchpropeller without requiring complicated and/or heavy mechanisms to drivethe blades to the desired pitch. In various embodiments, pitch may bevaried by varying the speed of rotation of the propeller.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, the invention is not limitedto the details provided. There are many alternative ways of implementingthe invention. The disclosed embodiments are illustrative and notrestrictive.

What is claimed is:
 1. A propeller for an aircraft, comprising: a hub; ablade including a neck portion angled away from a plane of rotation ofthe hub, wherein the blade has a longitudinal axis extending through acenter of the blade and running from a tip of the blade to an end of theneck portion; and a hinge including a pivotal link, the hinge connectingthe blade to the hub, wherein: the hinge has an axis of hinge rotationthat is offset from a line perpendicular to the longitudinal axis of theblade; and the hinge responds to forces acting on the blade to vary apitch of the blade including causing the blade to be at a lower pitchand higher dihedral angle in a vertical flight mode relative to aforward flight mode, the dihedral angle being an angle of the bladerelative to the plane of rotation of the hub.
 2. The propeller of claim1, wherein said hinge comprises a single pivotal link.
 3. The propellerof claim 1, wherein said hinge comprises a pin positioned on said axisof hinge rotation.
 4. The propeller of claim 1, wherein said hingepermits the blade to fold back towards a central axis of the hub if noforce is being applied to rotate the propeller.
 5. The propeller ofclaim 1, wherein said hinge is integrated with a structure mountedfixedly to said hub.
 6. The propeller of claim 5, wherein said structuremounted fixedly to said hub includes at least one tab portion.
 7. Thepropeller of claim 6, wherein said hinge comprises a pin positioned onsaid axis of hinge rotation and said pin runs through a transverse holein an end of the blade nearest to the hub and at least one hole on saidat least one tab portion.
 8. The propeller of claim 1, wherein said hubcomprises a nose cone.
 9. The propeller of claim 1, wherein said hubcomprises a nose structure.
 10. The propeller of claim 1, wherein thehinge is oriented in a plane that is in the plane of rotation of thehub.
 11. The propeller of claim 1, wherein the hinge comprises a forwardend associated with a leading edge of the blade and a rearward endassociated with a trailing edge of the blade, and wherein the forwardend lies further from a geometric center of the hub than the rearwardend.
 12. The propeller of claim 1, wherein the neck portion has a neckportion longitudinal axis that is substantially orthogonal to the axisof hinge rotation and wherein a substantial part of the blade is coupledto the hub by the neck portion.
 13. The propeller of claim 1, wherein asubstantial part of the blade comprises a primary airfoil portion of theblade.
 14. The propeller of claim 13, wherein the neck portion ispositioned between the primary airfoil portion and the hinge.
 15. Thepropeller of claim 1, wherein in a first propeller orientationassociated with a first mode of flight, the blade deploys to a firststable position associated with a first pitch, and in a second propellerorientation associated with a second mode of flight the blade rotatesabout the axis of hinge rotation to a second stable position associatedwith a second pitch.
 16. The propeller of claim 15, wherein the firstpropeller orientation comprises a substantially horizontal plane ofrotation.
 17. The propeller of claim 15, wherein the second propellerorientation comprises a substantially vertical plane of rotation. 18.The propeller of claim 15, wherein the first mode of flight correspondsto the vertical flight mode.
 19. The propeller of claim 15, wherein thesecond mode of flight corresponds to the forward flight mode.
 20. Thepropeller of claim 1, further comprising a stop that prevents the bladefrom moving beyond a point associated with the stop.